Method of cleaning a well bore prior to cementing

ABSTRACT

Aqueous and non-aqueous systems for cleaning a section of a subterranean well borehole and casing prior to cementing. A series of spacer fluids are introduced into the borehole to displace drilling fluid and to provide clean and water wet casing and borehole surfaces of the cleaned section of well bore. The cleaned section of the well bore will provide surfaces for superior bonding of the cement to the surfaces.

FIELD OF THE INVENTION

This invention relates to both aqueous and non-aqueous systems forcleaning a section of a subterranean well borehole and casing prior tocementing. A series of spacer fluids are introduced into the borehole todisplace drilling fluid and to provide clean and water wet casing andborehole surfaces of the cleaned section of well bore. The cleanedsection of the well bore will provide surfaces for superior bonding ofthe cement to the surfaces.

BACKGROUND OF THE INVENTION

The exploration of gas and oil involves drilling a borehole into theground through the geological formations of interest. Drilling mud isused to lubricate and cool the drill bit, to assist in bringing thedrill cuttings to the surface, to provide sufficient hydrostaticpressure within the well to prevent the bore collapsing under the forcesexperienced underground, and to prevent the influx of fluid from theformation while drilling. The drilling mud can be either aqueous basedor oil or synthetic based.

When the drilling of the borehole is completed a tubular known as acasing is secured within the borehole with cement. This insurespermanence of the borehole and it prevents entry of formation fluid,other than from the formation which is being produced. It is commonprocedure to pump the cement down the inside of the casing to the bottomand then up the outside of the casing, between the casing and theborehole wall, until it fills and lines the section of the annulus to becemented. That is, the space between the casing and the borehole wall.It is important that the cement lining be free of voids, that is,sections between the casing and borehole wall that is void of cement. Itis also important that the cement be well bonded to both the casing andborehole wall. If good bonding is not established between the cement andthe casing and borehole wall surfaces, then production from onereservoir could enter another and be lost; an undesirable fluid from onereservoir could enter the production zone of another; or the pumpedfluid of an injection well could end up in the wrong zone. To ensuregood bonding between cement and the appropriate surfaces, it isnecessary to remove substantially all traces of drilling mud on thecasing and the borehole wall. Incomplete mud removal can leave a channelbehind which could prevent total isolation of a production zone.Unfortunately, the substantial complete removal of mud often provesextremely difficult. Various methods and mechanisms have been devised inan attempt to achieve complete mud removal and to provide a completecement lining, free of voids, between the casing and the borehole wall.

One type of method includes the use of spacer fluids ahead of thecement. That is, liquids that will literally wash the mud off of thecasing and borehole wall. These fluids can be pumped so that they arepositioned between the cement and the mud. Such fluids can be of thetype known as "chemical washes" which are usually low-viscosity liquidscontaining surfactants and mud thinners, or diluents. They can also bethose known as "spacers", which are rather more viscous, gel-likeliquids that are primarily used to form a buffer between the cement andthe mud. Although it is not always clear in the literature whether aparticular fluid is a spacer or a chemical wash, a spacer is generallycharacterized as a thickened composition that functions primarily as afluid piston in displacing the mud. Frequently, spacers contain anappreciable amount of weighting materials, as well as fluid loss controlagents. Chemical washes, on the other hand, are generally thin, orrelatively non-viscous, fluids which are effective principally as aresult of turbulence, dilution, and surfactant action on the mud and mudfilter cake. Chemical washes may contain some solids to act as anabrasive, but the solids content is generally significantly lower thanin spacers because chemical washes are typically too low in viscosity tohave good solids carrying capacity. For purposes of the presentinvention, the term "spacer" or "spacer fluid" means both chemicalwashes as well as the more conventional meaning for the more viscousspacer fluids.

Aqueous based chemical washes are taught in U.S. Pat. No. 4,207,194.These chemical washes are of the type containing one or more of: (a) atleast one surfactant to remove water based drilling muds from aborehole; and (b) at least one surfactant to enhance the bonding ofcement to the wall of a borehole and the casing. There is also includedan effective amount of a fluid loss additive such as a mixture of atleast two oil soluble particulate resins, one of which remains hard andfriable, and the other of which is soft and pliable (at the temperatureto be encountered in the well) when dispersed in an aqueous medium.

U.S. Pat. No. 4,108,779 teaches a water-in-oil emulsion spacer fluidwhich is compatible with drilling fluids and cement compositions andwhich is comprised of a hydrocarbon oil, salt water, an emulsifier whichis comprised of a first and second fatty acid, and asurfactant-dispersant.

U.S. Pat. No. 5,101,902 teaches an aqueous spacer composition compatiblewith drilling muds and cement slurries which spacer composition iscomprised of a biopolymer selected from the group consisting ofscleroglucan and biopolymers produced by the bacteria Azotobacherindicus as an anti-settling means, a fluid loss controlling means, awetting agent selected from the group consisting of at least onepolyethoxyl ester of a C₉ -C₁₂ fatty acid, and a weighting means.

U.S. Pat. No. 4,588,032 teaches a fluid spacer composition for use inwell cementing, which composition is comprised of an aqueous fluid, anadmixture of nonylphenols ethoxylated with from 1 to 14 moles ofethylene oxide, and preferably, at least one member selected from thegroup consisting of a sulfonated linear C₈ to C₁₈ straight chain alcoholethoxylated with from 2 to 20 moles of ethylene oxide, a low molecularweight aliphatic glycol ether containing from about 3 to about 12 carbonatoms per molecule and an alcohol containing from 3 to 8 carbon atomsethoxylated with 2 to 4 moles of ethylene oxide together with anyconventionally utilized spacer additives, if desired, such asviscosifiers, weighting agents, and the like.

While there are various chemical washes and spacer fluids in commercialpractice today, there is still a need in the art for ever improvedtechniques for displacing drilling fluids and leaving the boreholesurfaces clean for adequate bonding of cement in the annular spacedefined by the casing and borehole wall.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided a method forcleaning a section of a well borehole prior to a cementing operation,said borehole having a casing suspended therein, and containing thereinan oil or synthetic-based drilling fluid, the method comprising:

a) displacing drilling fluid with a first spacer fluid from the sectionof said borehole to be cemented, said first spacer fluid comprised ofwater, an effective amount of solid particles for weighting, and fromabout 1 to 20 vol. % of a surfactant, wherein a polymeric component isused in amounts such that said first spacer fluid has a higher yieldpoint than the drilling fluid;

b) pumping into said borehole a second spacer fluid, under turbulentflow conditions, which second spacer fluid is comprised of a solventwith respect to drilling fluid residue in said borehole, and which isused in an amount to effectively remove and displace substantially allof any remaining drilling fluid residue and to displace said firstspacer fluid from the cleaned section of the borehole; and

c) pumping into said borehole a third spacer fluid which is awater-based composition comprised of an aqueous solution of a surfactantcomponent, wherein the amount of surfactant is about 1 to 20 vol. %,based on the total volume of said spacer fluid, and wherein said thirdspacer fluid is used in an amount that will effectively displacesubstantially all of said second spacer fluid and leave at least thecleaned section of said borehole substantially water wet.

In a preferred embodiment of the present invention the density of saidfirst spacer fluid is equal to or greater than the density of thedrilling fluid.

In another preferred embodiment of the present invention the viscosityof the first and third spacer fluid is increased with a naturallyoccurring gum or other polymeric material.

In yet another preferred embodiments of the present invention thepolymeric component is selected from xanthan gum, and a high molecularweight cellulose derivative such as carboxymethylcellulose (CMC),hydroxyethylcellulose (HEC), and hydroxypropylcellulose (HPC).

In still another preferred embodiment of the present invention thesurfactant is non-ionic and is selected from the group consisting ofamine oxides, ethoxylated or propoxylated nonyl phenols, ethoxylated orpropoxylated alkyl phenols, ethoxylated or propoxylated octyl phenols,ethoxylated or propoxylated dodecyl phenols, ethoxylated or propoxylatedprimary linear C₄ to C₂₀ + alcohols, polyethylene glycols of allmolecular weights and reactions, and polypropylene glycols of allmolecular weights and reactions.

Also in accordance with the present invention there is provided a methodfor cleaning a section of a borehole prior to a cementing operation,said borehole having a casing suspended therein, and containing thereinan oil or synthetic-based drilling fluid, the method comprising:

a) displacing drilling fluid with a first spacer fluid from the sectionof said borehole to be cemented, said first spacer fluid comprised of aweighted solvent, which solvent is an effective solvent with respect todrilling fluid residue in the borehole;

(b) pumping into said borehole, under turbulent flow conditions, asecond spacer fluid which is comprised of a solvent with respect todrilling fluid residue in the borehole, and which is used in an amountwhich is effective to remove and displace substantially all of anyremaining drilling fluid residue and said first spacer fluid from thesection of the borehole to be cemented;

(c) pumping into said borehole a third spacer fluid which is comprisedof an aqueous solution of a surfactant component, wherein the amount ofsurfactant is about 1 to 20 vol. %, based on the total volume of thefluid, and wherein the fluid is used in an amount that will effectivelydisplace substantially all of said second spacer fluid and leave thesection of the borehole to be cemented substantially water wet.

In another preferred embodiment of the present invention the solvent ofone or both of the first and second spacer fluids is a terpenehydrocarbon.

In a preferred embodiment of the present invention a diluent oil is usedprior to the introduction of said first spacer fluid of step (a) foreither one or both of the aqueous and the non-aqueous spacer systems toinitiate displacement of the drilling fluid.

In still another preferred embodiment of the present invention thediluent oil is selected from the group consisting of: a conventionalbase oil for drilling fluids, white mineral oils, paraffinic solvents,silicone oils, crude oils, distillates such as kerosenes and dieselfuels, gasolines, naphthas, alcohols, plant oils, and synthetic oilsincluding, but not limited to, esters and olefins.

In yet another preferred embodiment of the present invention the solventwhich is the base for any one or more of the spacer fluids for eitherthe aqueous system or the non-aqueous system is selected from theterpenes hydrocarbons.

Also in accordance with the present invention cement is pumped into theborehole after treatment with the spacer fluids, in such an amount todisplace any remaining spacer fluid and to fill the cleaned annularspace defined by the casing tubular and the borehole wall.

DETAILED DESCRIPTION OF THE INVENTION

It is be understood that the terms "drilling fluid" and "drilling mud"are used interchangeably herein. Drilling muds are typically classifiedbased on the composition of the liquid phase, such as: fresh-water,salt-water, emulsion, oil, and synthetic based. Synthetic based muds aremore biodegradable and more dispersible in seawater or brine, thantraditional oil base muds, however, they are more difficult to removefrom the metal surfaces of drilling equipment. Muds may be furtherclassified according to components, type of chemical treatment, orapplication. Drilling mud normally consists of the following fractions:

1. Liquid (water, oil, or both), which is the major fraction by volume.

2. Noncolloidal solids (sand, iron ore, barite, hematite), frequentlythe major component by weight.

3. Colloidal solids (clays, organic colloids), the major fraction indetermining performance and properties of the mud.

4. Dissolved chemicals (mineral lignin, barium carbonate, sodiumbicarbonate, formaldehyde, etc.) used to thicken muds and to controlfiltration.

The drilling muds which are of interest of cleaning from boreholes priorto cementing in the practice of the present invention are the oil basedmuds, both synthetic oils and natural based oils.

Before cementing well casings in a borehole, drilling mud must first beremoved, or displaced from the section of the borehole to which thecasing will be cemented. Contact between cement and the drilling fluidis be avoided because the two are typically incompatible and oftenresults in detrimental interactions. This incompatibility can contributeto failure to obtain a satisfactory bond between the cement and the wallof the borehole and between the cement and the casing. In applicationswhere oil-based drilling fluids are used, the incompatibility oftenresults in contamination, or commingling, of mud with cement, and cementwith mud. Extreme viscosities often arise from such commingling, causingexcessive pressures and pumping problems. In some cases this leads toundesirable formation breakdown. When a portion of the drilling fluid iscommingled with cement premature setting of the cement can occur andconversely, when drilling fluids are contaminated with cement, theproperties advantageously characteristic of drilling fluids areadversely affected. The problem of commingling can be overcome byseparating the cement and the drilling fluid by what is called a"spacer" fluid. Furthermore, it is the function of these spacer fluidsto clean the borehole to such a degree a to provide good bonding betweenthe cement and the casing and the borehole wall.

As previously mentioned, it is preferred that the present invention beused in wells in which oil or synthetic based drilling fluids (muds) areemployed. Among the problems associated with drilling muds is that theliquid phase of the drilling mud tends to flow from the well intoexposed permeable formations with the result that mud solids arefiltered out on the wall of the borehole and a filter cake of mud-likematerial is formed thereon. This mud-like material is a barrier toproper bonding of cement which is needed to produce an impermeable bondbetween the casing and the borehole wall. In an ideal cementingoperation the filter cake would be removed from the borehole wall andreplaced by the cement slurry to permit the formation of a solid layerof hardened, cured and bonded cement between the casing and the geologicformation through which the borehole passes. It is very difficult toadequately remove filter cake from a borehole, and often the borehole isnot sufficiently clean for the cementing operation. In such casesremedial cement squeeze operations must be used, which are extremelycostly and which may also be harmful to the production of the well. Thespacer systems of the present invention will leave the borehole wall andthe casing clean of residual mud and filter cake. They will also providesaid surfaces with enhanced water wet properties which enhance bondingof the aqueous based cement to the casing and the borehole wall.

Any oil and/or gas borehole can be cleaned in accordance with thepresent spacer systems regardless of their angle or deviation fromvertical to horizontal. Cleaning the well bore, or a section of the wellhole, containing a casing, in accordance with the present invention willresult in the desired zonal isolation, good cement-to-casing bonding andgood cement-to-wall bonding. Thus any remedial cement squeeze operationswill be unnecessary.

The present invention relates to both an aqueous and a non-aqueousspacer system for cleaning the section of a well borehole in which acasing is to be cemented. The aqueous spacer system is comprised ofthree spacer fluids, the first being a weighted aqueous basedsurfactant, preferably a non-ionic surfactant fluid, the second being anorganic solvent based fluid, and the third being an aqueous basedsurfactant fluid which leaves the borehole water wet. The non-aqueousspacer system is also comprised of three spacer fluids, the first beinga weighted solvent fluid, the second being an organic solvent basedfluid, and the third being an aqueous based surfactant, preferably anon-ionic surfactant fluid which leaves the borehole water wet.

The first spacer fluid of the aqueous system is pumped into the wellbore to displace that portion of drilling fluid in the annulus of theborehole to be subsequently cemented, and to start the cleaning process.This first spacer is a relatively high viscosity, high yield point waterbased spacer containing particulate weighting material and a surfactant,preferably a non-ionic surfactant. This first spacer will initiate waterwetting of the borehole wall and casing. Further, this first spacerwill: (a) have a density less than, or equal to, or greater than,preferably equal to or greater than, the density of the drilling fluid,(b) have a higher yield point than the drilling fluid, and (c) be used,in volume of barrels, of from 1 to 200%, preferably from about 1 to 100%of annular space between the borehole wall and the casing. The "yieldpoint" of a drilling fluid is a measurement under flowing conditions ofthe force in drilling fluid that causes gel structure to develop whenthe drilling fluid is at rest. This first spacer will also contain fromabout 1 to about 20%, based on the total volume of said first spacer, ofa surfactant, preferably a non-ionic surfactant. Non-limiting examplesof non-ionic surfactants which may be used in the practice of thepresent invention include those selected from the group consisting ofamine oxides, ethoxylated or propoxylated nonyl phenols, ethoxylated orpropoxylated alkyl phenols, ethoxylated or propoxylated octyl phenols,ethoxylated or propoxylated dodecyl phenols, ethoxylated or propoxylatedprimary linear C₄ to C₂₀ + alcohols, polyethylene glycols of allmolecular weights and reactions, and polypropylene glycols of allmolecular weights and reactions. Preferred are ethoxylated octylphenols, polypropylene glycols, ethoxylated linear alcohols, andethoxylated nonyl phenols. More preferred are ethoxylated linearalcohols, and ethoxylated nonyl phenols. The spacer will need apolymeric component. The polymeric component is selected from xanthangum, and a high molecular weight cellulose derivative such ascarboxymethylcellulose (CMC), hydroxyethylcellulose (HEC), andhydroxypropylcellulose (HPC).

Solids suitable for use herein as weighting agents are those which areconventionally used in the drilling industry and which are substantiallywater and liquid hydrocarbon insoluble. Non-limiting examples of suchsolids include bentonite, diatomaceous earth, barite, hematite or otheriron oxides, fly ash, other finely ground solids, and the like. Theweighting agents can also serve as scrubbing agents. The weighting agentis used in an amount sufficient to provide the desired compositiondensity. The particle size of the solids used herein are any size whichis conventionally used for drilling fluids and spacers. For example,clay, or bentonite particles are typically extremely fine and range fromabout 0.05 to 5 microns, averaging about 0.5 microns. Fly ash particles,on the other hand, are on the order of about 100 times greater than thatof bentonite, or about 0.5 to 200 microns, averaging about 50 microns.The precise particle size used for weighting the spacer fluids of thepresent invention is not important as long as the spacer fluids meettheir intended objective.

The second spacer of the aqueous system is used to detach and displacedrilling fluid residue and to displace said first spacer fluid. Thissecond spacer, which is pumped into the borehole under turbulentconditions, is a solvent which is capable of chemically detaching, ordissolving, drilling fluid residue from the casing and the boreholewall. The density of this second spacer will be from about 7 pounds pergallon (ppg) to about 20 ppg. This second spacer can also includeweighting material, but it should be realized that as the viscosity isincreased turbulent flow will be reduced. The viscosity of this secondspacer will preferably be less than about 2 cps. Non-limiting examplesof solvents which can be used as this second spacer include: glycols,such as propylene glycol, ethylene glycol, hexylene glycol, dipropyleneglycol, diethylene glycol, tripropylene glycol, and triethylene glycol;poly glycols; ethers, such as monomethyl ether; glycol ethers; alkanesand cyclic alkanes, such as pentane, hexane, and cyclohexane, heptane;mineral oils, such as seal oil; plant oils, such as the terpenes (whichare preferred); esters; aromatics, such as benzene, toluene, xylene, andethyl benzene; ketones, such as acetone, methyl ethyl ketone, methylpropyl ketone, methyl isobutyl ketone, methyl isoamyl ketone, diacetonealcohol, methyl amyl ketone, cyclohexanone, diisobutyl ketone, andisophorone; chlorinated solvents, such as methylene chloride;chloroform, 1,1,1-trichlorethane, ethylene dichloride, trichlorethylene,propylene dichloride, perchlorethylene, monochlorobenzene, andorthodichlorobenzene; amines, such as isopropyl amine, ethyl amine,diethyl amine, butyl amine, diisopropyl amine, triethyl amine,morpholine, cyclohexylamine, dimethylethanoamine, dibutyl amine,tetraethylene pentamine, momoisopropanolamine, diethylethanoamine,monoethanolamine, diethanolamine, diisopropanolamine; alcohols, such asmethanol, ethanol, isopropanol, n-propanol, isobutanol, n-butanol, amylalcohol, methyl amyl alcohol, cyclohexanol, and 2-ethylhexanol; andpetroleum naphthas.

The third spacer of the aqueous system is pumped down the well bore,preferably at turbulent conditions. It will displace at least a portion,preferably substantially all, of said second spacer fluid and remove anyremaining solids. It will also finalize the water wetting process. Thisthird spacer can be a viscosified composition, or a non-viscosifiedcomposition. Both the viscosified and the non-viscosified forms cancontain from about 1 to about 20 vol. % of a water based surfactant,preferably a non-ionic surfactant. The third spacer can be viscosified,and if so it can be weighted to be from about 8 to 20 pounds per gallon.Weighting materials suitable for use with this third spacer are any ofthose conventionally used in the drilling industry, and whichnon-limiting list was set forth previously herein. The volume of thirdspacer used will be from about 1 to 200%, preferably from about 1 to100% of annular space between the borehole and casing. The water usedfor this third spacer fluid composition can be salt water or freshwater. This third spacer can also be viscosified with a polymericcomponent if a more viscous composition is needed. Non-limiting examplesof polymeric materials suitable for use herein include xanthan gum, andhigh molecular weight cellulose derivatives such ascarboxymethylcellulose (CMC), hydroxyethylcellulose (HEC), andhydroxypropylcellulose (HPC). Preferred are xanthan gum and HEC. Thisspacer may also contain the previously mentioned surfactants.

As previously mentioned, the present invention also relates to anon-aqueous spacer system for treating, or cleaning, a well boreholeprior to cementing. The non-aqueous spacer system of the presentinvention is comprised of a series of three spacer fluids. The firstspacer fluid is pumped into the borehole to displace that portion of thedrilling fluid in the annulus of the borehole to be subsequentlycemented, and to start the cleaning process. This first spacer is asomewhat high viscosity weighted solvent spacer characterized as having:(a) a density less than, equal to or greater than, preferably equal toor greater than the density of the drilling fluid, (b) be used, in avolume of barrels of from 1 to 200%, preferably from about 1 to 100% ofannular volume between the bore hole wall and the casing. Weightingmaterials suitable for use with this first spacer are any of thoseconventionally used in the drilling industry and which non-limiting listwas set forth previously herein. The viscosity of this first spacerfluid for the non-aqueous system can be increased, preferably with arelatively short chain oil-soluble polymer material. The solvent is thesame as used for the second spacer fluid in both the aqueous and thenon-aqueous systems herein. That is, it is a solvent with respect todrilling fluid, or mud, residue in the borehole being cleaned.

The second spacer of the non-aqueous system is used to detach anddisplace drilling fluid residue and to displace said first spacer fluid.This second spacer, which is pumped into the borehole under turbulentconditions, is a solvent which is capable of chemically detaching ordissolving drilling fluid residue from the casing and the borehole wall.The viscosity of the second spacer will preferably be less than about 2cps. Non-limiting examples of solvents which can be used as this for allof the solvent spacer fluids of the present invention include: glycols,such as propylene glycol, ethylene glycol, hexylene glycol, dipropyleneglycol, diethylene glycol, tripropylene glycol, and triethylene glycol;poly glycols; ethers, such as monomethyl ether; glycol ethers; alkanesand cyclic alkanes, such as pentane, hexane, and cyclohexane, heptane;mineral oils, such as seal oil; plant oils, such as the terpenes (whichare preferred); esters; aromatics, such as benzene, toluene, xylene, andethyl benzene; ketones, such as acetone, methyl ethyl ketone, methylpropyl ketone, methyl isobutyl ketone, methyl isoamyl ketone, diacetonealcohol, methyl amyl ketone, cyclohexanone, diisobutyl ketone, andisophorone; chlorinated solvents, such as methylene chloride;chloroform, 1,1,1-trichlorethane, ethylene dichloride, trichlorethylene,propylene dichloride, perchlorethylene, monochlorobenzene, andorthodichlorobenzene; amines, such as isopropyl amine, ethyl amine,diethyl amine, butyl amine, diisopropyl amine, triethyl amine,morpholine, cyclohexylamine, dimethylethanoamine, dibutyl amine,tetraethylene pentamine, momoisopropanolamine, diethylethanoamine,monoethanolamine, diethanolamine, diisopropanolamine; alcohols, such asmethanol, ethanol, isopropanol, n-propanol, isobutanol, n-butanol, amylalcohol, methyl amyl alcohol, cyclohexanol, and 2-ethylhexanol; andpetroleum naphthas.

The third spacer of the non-aqueous system, which is substantially thesame as the third spacer fluid for the aqueous system herein, is pumpeddown the borehole, preferably in turbulent conditions. It will displaceat least a portion, preferably substantially all, of said second spacerfluid and remove any remaining solids. It will also finalize the waterwetting process. This third spacer can be a viscosified composition, ora non-viscosified composition. Both the viscosified and thenon-viscosified forms can contain from about 1 to about 20 vol. % of awater based surfactant, as previously listed for the aqueous systemabove. This spacer can be viscosified, and it can also be weighted fromabout 8 to 20 pounds per gallon. Weighting materials suitable for usewith this spacer are any of those conventionally used in the drillingindustry, and which non-limiting list was set forth previously herein.The volume of this spacer will be from about 1 to 200%, preferably fromabout 1 to 100% of annular volume between the borehole wall and thecasing. The water used for this spacer fluid composition can be saltwater or fresh water. This third spacer can also be viscosified with apolymeric component if a more viscous composition is needed.Non-limiting examples of polymeric materials suitable for use hereininclude xanthan gum, and high molecular weight cellulose derivativessuch as carboxymethylcellulose (CMC), hydroxyethylcellulose (HEC), andhydroxypropylcellulose (HPC). Preferred are xanthan gum and HEC.

This second spacer fluid, as well as the second spacer fluid of theaqueous spacer system, is used under turbulent conditions and iseffective for chemically detaching mud residue from the casing and themud cake from the borehole. These spacers are in contact with the wellbore for an effective amount of time. That is, for a time which iseffective to remove substantially all of the residual mud residue andmud cake from the borehole. This amount of time will typically be fromabout 1 to 15 minutes, preferably from about 1 to 10 minutes.

All spacer fluids, both for the aqueous and the non-aqueous systems mayalso include other materials for their known purposes, such askaolinite, gilsonite, cellophane flakes, and the like for lostcirculation control, provided they do not render the spacer incompatiblewith the mud or the cement and provided they do not interfere with thedesired turbulent flow of the spacers. Where a cement is to contain alost circulation material, for instance, the same material may beemployed in the spacer. Minor amounts of an antifoaming agent may beincluded to provide better mixing properties, e.g., up to about 1percent by weight of water. Where a formation is present which issensitive to fresh water, such as certain shales or clay containingsandstone, a salt such as an alkali metal halide may be incorporated inthe spacer.

In the embodiments of the present invention for both the aqueous and thenon-aqueous systems, a diluent oil may be first pumped down the boreholeto dilute the drilling fluid and to initiate displacement of thedrilling fluid. By "diluent oil" we mean an organic liquid, preferablyan oil, which is substantially the same as, or is compatible with, theoil which is used as the base for the drilling fluid in the boreholebeing treated. Non-limiting examples of organic liquids that can be usedas the diluent oil include the base-oil of the drilling mud of theborehole being serviced, as well as crude oils, distillate oils,gasolines, naphthas, kerosenes, fuel oils, white oils, oils derived fromcoal or shale, aromatic oils, silicone oils, mineral seal oils, alcoholsand paraffinic solvents. Also suitable as a diluent are vegetable oilswhich include babassu oil, castor oil, coconut oil, corn oil, cottonseedoil, hemp oil, linseed oil, oiticica oil, olive oil, palm oil, peanutoil, rape oil, safflower, sesame oil, soybean, sunflower, and tung oil,and synthetic oils. Also suitable are the terpenes, preferably limoneneand terpinol. Other terpene related derivatives composed of carbon,hydrogen, and oxygen, and having 10 carbon atoms with 0, 1 or 2 hydroxylgroups, and 0, 1 or 2 double bonds, may be used in alternateembodiments. The hydroxyl group helps break the hydrogen bonding ofsludge to metal surfaces. The terpene alcohols are effective indispersion or emulsion systems. Synthetic oils are a preferred class ofcompounds for use as the diluent oil, especially esters, diethers,olefins, and detergent alkylate, as well as mixtures thereof. Syntheticoils also include hydrocarbon oils and halo-substituted hydrocarbon oilssuch as polymerized and nterpolymerized olefins, for examplepolybutylenes, polypropylenes, propylene-isobutylene copolymers,chlorinated polybutylenes, poly(1-hexenes), poly(1-octenes),poly(1-decenes); alkylbenzenes, such as dodecylbenzenes,tetradecylbenzenes, dinonylbenzenes, di-(2-ethythexyl)benzenes;polyphenyls such as biphenyls, terphenyls, and alkylated polyphenyls;and alkylated diphenyl ethers and alkylated diphenyl sulfides andderivatives, analogs and homologs thereof.

After the drilling fluid has been displaced and the borehole wall andcasing cleaned in accordance with the present invention, the casing canbe cemented to the bore walls by conventional means.

From the foregoing, it will be apparent that there has been hereindescribed a process for removing drilling fluid materials from aborehole which is especially effective prior to the introduction ofaqueous fluid cement for improved cement bonding results. Variouschanges and alterations may be made in the practice of this process bythose skilled in the art without departing from the spirit of theinvention. It is intended that such changes be included within the scopeof the appended claims.

What is claimed is:
 1. A method for cleaning a section of a well boreprior to a cementing operation, said well bore having a casing suspendedtherein, and containing therein an oil or synthetic-based drillingfluid, the method comprising:a) displacing drilling fluid with a firstspacer fluid from the section of said borehole to be cemented, saidfirst spacer fluid comprised of water, an effective amount of solidparticles for weighting, and from about 1 to 20 vol. % of a surfactant,wherein a polymeric component is used in amounts such that said firstspacer fluid has a higher yield point than the drilling fluid; b)pumping into said borehole a second spacer fluid, under turbulent flowconditions, which second spacer fluid is comprised of a solvent withrespect to drilling fluid residue in said borehole, and which is used inan amount to effectively remove and displace substantially all of anyremaining drilling fluid residue and to displace said first spacer fluidfrom the cleaned section of the well bore; and c) pumping into saidborehole a third spacer fluid which is a water-based compositioncomprised of an aqueous solution of a surfactant component, wherein theamount of surfactant is about 1 to 20 vol. %, based on the total volumeof said spacer fluid, and wherein said third spacer fluid is used in anamount that will effectively displace substantially all of said secondspacer fluid and leave at least the cleaned section of said boreholesubstantially water wet.
 2. The method of claim 1 wherein prior to theintroduction of any spacer fluid an effective amount of a diluent oil isintroduced into said borehole to dilute the drilling fluid and toinitiate the displacement of the drilling fluid from the borehole. 3.The method of claim 1 wherein the density of the first spacer fluid isequal to or greater than the density of the drilling fluid.
 4. Themethod of claim 3 wherein, the diluent oil is selected from the groupconsisting of: a conventional base oil for drilling fluids, whitemineral oils, paraffinic solvents, silicone oils, crude oils,distillates, gasolines, naphthas, alcohols, and synthetic oils.
 5. Themethod of claim 1 wherein the viscosity of the first spacer and thethird spacer fluid is increased with a naturally occurring gum or apolymeric material.
 6. The method of claim 4 wherein the polymericcomponent is selected from xanthan gum, and a high molecular weightcellulose derivative such as carboxymethylcellulose (CMC),hydroxyethylcellulose (HEC), and hydroxypropylcellulose (HPC).
 7. Themethod of claim 1 wherein the surfactant of the first spacer and thethird spacer is a non-ionic surfactant and is selected from the groupconsisting of amine oxides, ethoxylated or propoxylated nonyl phenols,ethoxylated or propoxylated alkyl phenols, ethoxylated or propoxylatedoctyl phenols, ethoxylated or propoxylated dodecyl phenols, ethoxylatedor propoxylated primary linear C₄ to C₂₀ + alcohols, polyethyleneglycols of all molecular weights and reactions, and polypropyleneglycols of all molecular weights and reactions. Preferred areethoxylated octyl phenols, polypropylene glycols, ethoxylated linearalcohols, and ethoxylated nonyl phenols. More preferred are ethoxylatedlinear alcohols, and ethoxylated nonyl phenols.
 8. The method of claim 1wherein the solvent comprising said second spacer is selected from thegroup consisting of glycols, ethers, esters, linear alkanes, cyclicalkanes, mineral oils, plant oils, aromatics, ketones, chlorinatedsolvents, amines, alcohols, petroleum naphthas and terpene hydrocarbons.9. The method of claim 8 wherein the solvent is a terpene hydrocarbon.10. The method of claim 1 wherein said first spacer fluid is alsoweighted with an effective amount of solids material.
 11. A method forcleaning a section of a borehole prior to a cementing operation, saidborehole having a casing suspended therein, and containing therein anoil or synthetic-based drilling fluid, the method comprising:a)displacing drilling fluid with a first spacer fluid from the section ofsaid borehole to be cemented, said first spacer fluid comprised of aweighted solvent, which solvent is an effective solvent with respect todrilling fluid residue in the borehole; (b) pumping into said borehole,under turbulent flow conditions, a second spacer fluid which iscomprised of a solvent with respect to drilling fluid residue in theborehole, and which is used in an amount which is effective to removeand displace substantially all of any remaining drilling fluid residueand said first spacer fluid from the section of the borehole to becemented; (c) pumping into said borehole a third spacer fluid which iscomprised of an aqueous solution of a surfactant component, wherein theamount of surfactant is about 1 to 20 vol. %, based on the total volumeof the fluid, and wherein the fluid is used in an amount that willeffectively displace substantially all of said second spacer fluid andleave the section of the borehole to be cemented substantially waterwet.
 12. The method of claim 11 wherein prior to the introduction of anyspacer fluid an effective amount of a diluent oil is introduced intosaid borehole to dilute the drilling fluid and to initiate thedisplacement of the drilling fluid from the borehole.
 13. The method ofclaim 12 wherein the diluent oil is selected from the group consistingof: a conventional base oil for drilling fluids, white mineral oils,paraffinic solvents, silicone oils, crude oils, kerosenes, distillates,gasolines, naphthas, alcohols, plant oils, and synthetic oils, includingbut not limited to, esters and olefins.
 14. The method of claim 11wherein the viscosity of the third spacer fluid is increased with anaturally occurring gum or a polymeric material.
 15. The method of claim14 wherein the polymeric component is selected from xanthan gum, and ahigh molecular weight cellulose derivative such ascarboxymethylcellulose (CMC), hydroxyethylcellulose (HEC), andhydroxypropylcellulose (HPC).
 16. The method of claim 11 wherein thesurfactant of the third spacer is a non-ionic surfactant and is selectedfrom the group consisting of amine oxides, ethoxylated or propoxylatednonyl phenols, ethoxylated or propoxylated alkyl phenols, ethoxylated orpropoxylated octyl phenols, ethoxylated or propoxylated dodecyl phenols,ethoxylated or propoxylated primary linear C₄ to C₂₀ + alcohols,polyethylene glycols of all molecular weights and reactions, andpolypropylene glycols of all molecular weights and reactions. Preferredare ethoxylated octyl phenols, polypropylene glycols, ethoxylated linearalcohols, and ethoxylated nonyl phenols. More preferred are ethoxylatedlinear alcohols, and ethoxylated nonyl phenols.
 17. The method of claim11 wherein the solvent comprising said first spacer fluid and saidsecond spacer fluid is selected from the group consisting of glycols,ethers, esters, linear alkanes, cyclic alkanes, mineral oils, plantoils, aromatics, ketones, chlorinated solvents, amines, alcohols,petroleum naphthas, and terpene hydrocarbons.
 18. The method of claim 17wherein the solvent is a terpene hydrocarbon.